This invention relates to washing apparatus and method for assaying samples of blood, urine or other body fluids for antigens or their antibodies. More particularly, this invention relates to diagnostic apparatus for a direct assay using enzymes, fluorochromes, or radioisotopes to determine the presence of hepatitis associated antigen or its antibodies having at least two free antigenically active sites.
Although there have been methods for determining the presence of antigenically active molecules such as intact viruses, virus capsids, bacteria, hormones, haptens, etc., the known immunochemical tests require a number of discrete washing steps. For example, in testing for hepatitis associated (Hepatitis B Surface Antigen HB.sub.s Ag), hepatitis antibody supported on an appropriate such as a bead is contacted with an unknown serum. Following incubation, the serum must be removed from the reaction vessel by aspiration followed by inserting wash fluid and then aspirating a second time to remove the fluid. This washing step is frequently repearted five or six times and is tedious and time-consuming. The volume of wash fluid used in each discrete washing is, of course, limited by the volume of the reaction vessel. Additionally, with each aspiration step, a small volume of fluid remains behind on the sides of the vessel or in the bottom portion. When wash fluid is again added, this residue is diluted; however, on subsequent aspiration, a small portion of the diluted residue remains behind. Because of the dilution factor, it is frequently necessary to carry out the washing steps (with aspiration) five and six times to reduce the residue to levels which will not interfere with subsequent reaction steps. Additionally, as other reagents are added, it is necessary to repeat the whole washing procedure.
What is needed is a relatively quick process for washing to remove reagents from the reaction vessel. The process must also be thorough so that little, if any, residue is left behind. Presently available apparatus and methods are limited by the volume of the reaction vessel, and, because of the dilution factor mentioned above, a thorough wash will require a relatively large volume of fluid greatly in excess of the volume of the reaction vessel. Therefore, a number of discrete and time-consuming wash-aspirating steps are required.
Another problem encountered with discrete washing steps is over-flow; i.e., the clinician must be careful not to insert too much wash water. If the test tube or other apparatus overflows, surrounding test tubes or even those present in the laboratory could be contaminated. Additionally, the reaction vessel is usually open to the atmosphere giving rise to the possibility of aerosolization of highly infectious reactants.
It is the principal object of the present invention to provide diagnostic apparatus which accomplishes a quick and thorough washing in a single step without requiring a number of discrete and time-consuming wash-aspiration steps. Any desired amount of washing fluid can be employed as is necessary to achieve a thorough wash even though the fluid volume is greatly in excess of the volume of the reaction vessel.
In addition to overcoming the problems of dilution and the time-consuming washing steps, the apparatus and method also prevents aerosolization of the reagents and eliminates the problem of over-flow.
Another attractive feature of the invention is that it is relatively simple in design and easy to assembly. These features are important in making the invention available on a mass basis.